1. Field of the Invention
The present invention relates generally to medical methods and devices. More particularly, the invention relates to methods and systems for removing hair by ablation of hair follicles.
Over the years, hair removal has been accomplished by a variety of temporary and permanent techniques. Tweezers, wax, sticky tape, and similar methods have been used to pull hair from its root beneath the skin. Such hair removal, however, is only temporary and the hair will soon regrow in the same location. Permanent hair removal may be accomplished by destroying the hair follicle which provides for new hair growth. The most common methods for achieving such permanent hair removal are electrolysis and the use of short pulsed light. Electrolysis requires inserting a wire into the same pore as the hair, advancing the wire until the operator feels some resistance caused by the hair follicle, and then applying an electric pulse. The electric pulse destroys the follicle preventing regrowth after the hair falls out. While effective, the introduction of a needle into the pore is uncomfortable for the patient, requires a high degree of skill by the operator, and is very time-consuming.
In contrast, short light pulses can be used to illuminate patches of skin at high intensity to heat and destroy all the hair present in that patch. While representing an enormous saving of time, the light functions by transmitting heat through the individual hairs to the hair follicle. Due to differences in skin and hair pigmentation, the results of such heat generation and absorbance can be highly variable, and the method is not successful in patients with dark skin, light hair color, or on very fine hair of any color.
A third technique has recently been proposed in U.S. Pat. No. 6,200,326. Instead of delivering electrical energy through a needle, ultrasonic energy may be delivered to individual hair follicles by advancing a needle through a pore to a hair follicle. While potentially effective, this method suffers from the same drawbacks and disadvantages discussed above with respect to hair removal by needle electrolysis.
For these reasons, it would be desirable to provide alternative and improved methods for permanently removing hair from a patient's skin. It would be particularly desirable if such methods and systems could destroy hair follicles without the need to introduce a needle or other apparatus through the associated hair pores and without relying on thermal or other energy transmission properties of the individual hairs. Such methods and systems should preferably be relatively simple to use and not require extensive training on the part of operators. Additionally, it would be particularly desirable if the methods could treat hair follicles which, at the time of the procedure, are in their telogen phase or without hair for other reasons. At least some of these objectives will be met by the inventions described hereinbelow.
2. Description of the Background Art
Use of a needle to deliver ultrasonic energy to disrupt hair follicles is described in U.S. Pat. No. 6,200,326 B1. Skin rejuvenation by ablating a plurality of subcutaneous sites with an array of ultrasonic transducers is described in U.S. Pat. No. 6,595,934 B1. Lysing adipose tissue using an externally focused high energy ultrasound transducer is described in U.S. Patent Application Publication No. 2003/0083536A1 and WO 02/054018A2. The full disclosures of each of these prior publications are incorporated herein by reference.